Site Assessment for Solar Water Heating Systems: Page 3 of 4

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Proper planning is important to maximize system performance.
Ideally, solar thermal collectors should be positioned to get full sun between 9 a.m. and 3 p.m. solar time. Proper planning is important to maximize system performance.
Street-level view
Street-level views can assist with identifying site-specific characteristics, such as roof type and roof slope, and potential shading issues.
Aerial photo
Aerial photos from online maps can also be used to spot potential shading issues. In addition, they can help the assessor determine the building’s orientation.
Solmetric’s free online Roof Azimuth Tool
Solmetric’s free online Roof Azimuth Tool can calculate a roof’s orientation angle with two clicks of a mouse.
Fitting additional solar equipment into an existing utility room
Fitting additional solar equipment into an existing utility room can be a challenge and may affect system design.
replace damaged or old roofing
Since an SWH system is designed to function for at least 20 years, it may be best to replace damaged or old roofing material prior to the system’s installation.
Solmetric’s iPV app
Solmetric’s iPV app offers a sample shade analysis for a site in San Francisco showing a 20% annual loss due to shade.
Solmetric’s iPV app
Solmetric’s iPV app allows users to trace obstructions on-screen to determine the site’s effective skyline.
Solmetric’s SunEye
Solmetric’s SunEye is a digital interface that provides detailed information about a site’s solar access.
Example SunEye Site Data
Solmetric’s SunEye is a digital interface that provides detailed information about a site’s solar access, expressing it as a monthly, biannual, and annual percentage.
The Solar Pathfinder’s Sun Trace Wizard
The Solar Pathfinder’s Sun Trace Wizard allows users to trace the shadows of obstructions from a digital photo, and then calculates monthly solar access.
The Solar Pathfinder solar assessment tool
The Solar Pathfinder solar assessment tool can be used manually (users trace the outline of obstructions reflected on the plastic dome onto the black sun path diagram) or an image can be imported into software for automated calculations.
Proper planning is important to maximize system performance.
Street-level view
Aerial photo
Solmetric’s free online Roof Azimuth Tool
Fitting additional solar equipment into an existing utility room
replace damaged or old roofing
Solmetric’s iPV app
Solmetric’s iPV app
Solmetric’s SunEye
Example SunEye Site Data
The Solar Pathfinder’s Sun Trace Wizard
The Solar Pathfinder solar assessment tool

Will the storage tank fit? It is important to verify that a preferred tank will actually fit. In addition to checking that there is sufficient clearance, door widths are checked to ensure the tank can be maneuvered into place.

Will changes to existing systems be required? Existing plumbing or electrical code violations should be addressed before the new system is installed.

Are there any red flags? Some issues don’t lend themselves to remote observation. For instance, is the roof sound enough to hold a system for 25 to 30 years? Are there major code violations or safety concerns with the existing water heating system? Will there be significant extra costs due to the need for electrical upgrades or complicated piping runs?

Shading Assessment Tools

Another key detail that can be observed during a site visit is the impact of shading. A shading assessment may be required for local incentives such as state tax credits or utility rebates.

Handheld digital devices and smartphones can use apps such as Solmetric’s iPV (for iPhone; $39.99) and Comoving Magnetic’s Solar Shading (for Android; $16) to measure the amount of shading at a site. They can provide a reasonable shade profile for homeowners who don’t need a professional shading assessment tool for a single installation.

When I went out to the tree-shaded site mentioned above, all I had with me was iPV. After using it for a few minutes on the roof, I returned to the ground with a shading profile of the site. For 80% of the year, the roof received no sun. The architect arrived, and I attempted to tactfully address the situation. After introductions and a couple of clarifying questions about why I had requested her presence, I explained that the trees on the neighbor’s property were going to be an issue.

I discussed sun angles and the performance of shaded collectors while trying to restrain my inner-Mainer, who occasionally defaults to an unhealthy dose of sarcasm. The architect was initially skeptical of my assessment, until I pulled the iPhone out of my pocket and showed her the results.

Designed primarily for assessing PV sites, the Solmetric SunEye 210 ($1,995) is a handheld device that includes a fish-eye camera and a touch screen for operation. The site assessor can input information about the project, such as the collector’s tilt and azimuth and the site’s coordinates. Once this information is entered, the touch screen displays a view through the fish-eye lens, a digital compass, and a digital level. While the SunEye is level and oriented to true south, the operator captures the fish-eye image. The device then compiles the data, overlaying a silhouette of the obstructions on a diagram that illustrates the sun’s position in the sky throughout the year.

From this, the SunEye calculates the percentage of available solar radiation at the site during each month and over the course of the year. The calculations are presented almost instantaneously and can help an installer make decisions on the fly. For instance, the site assessor can modify the graphic by erasing trees to determine how tree removal would affect shading. Solmetric offers PV Designer software that syncs with the SunEye data to aid in solar-electric system design, but does not offer a comparable program for SWH systems. Instead, the data must be entered into separate solar heating modeling software, such as RETScreen, F-Chart, T-Sol, Polysun, or the Solar Pathfinder Assistant (SPA; see below).

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